HR: 0800h
AN: T11A-0349    [Abstracts]
TI: What controls the earthquake and tsunami sources in subduction zone? MCS profiles across the Tokachi-oki earthquake sources along the Kuril Trench
AU: * Okamura, Y
EM: okamura-y@aist.go.jp
AF: Active Fault Research Center GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Tsujino, T
EM: taphonomy@ni.aist.go.jp
AF: Institute of Geoinformation and Geoscience GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Arai, K
EM: ko-arai@aist.go.jp
AF: Institute of Geoinformation and Geoscience GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Satake, K
EM: kenji.satake@aist.go.jp
AF: Active Fault Research Center GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Sasaki, T
EM: tmsasaki@mail.ecc.u-tokyo.ac.jp
AF: Department of Geosystem Engneering, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Ikehara, K
EM: k-ikehara@aist.go.jp
AF: Institute of Geoinformation and Geoscience GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Noda, A
EM: Noda Atsushi a.noda@aist.go.jp
AF: Institute of Geoinformation and Geoscience GSJ/AIST, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AB: High-resolution multi-channel seismic profiles show a contrast in active geologic structure in forearc slopes of the Kuril subduction zone, which reflects the mechanical processes along the plate boundary and the source regions of the recent earthquakes and tsunamis. Structural and tectonic patterns are different to the east and west of Kushiro submarine canyon along the southwestern Kuril trench, where recurrence of large (Msim8) earthquakes have been documented in the last 200 years. The source regions of recent earthquakes and tsunamis, 2003, 1952 and 1843, seem to be variable. The most recent two events, 1952 and 2003, shared the same asperity beneath the forearc slope to the west of Kushiro Submarine Canyon, according to seismological analysis (Yamanaka and Kikuchi, 2003). However, their tsunami sources were different; the 1952 tsunami source extended to the lower slope east of the canyon, according the inversion of tide gauge records (Hirata et al., 2003). While the data were limited, the tsunami height distribution of the 1843 earthquake was similar to that of the 1952 event. We performed high-resolution multi-channel seismic surveys on both upper and lower forearc slopes of southwestern Kuril Trench. The upper slope was surveyed during 2002-2004 R/V Hakurei cruises, while the lower slope was covered during JAMSTEC's R/V Kairei cruise in 2005. These profiles indicate a subsiding forearc basin covered by > 3 km thick Neogene sediments around the Tokachi-oki asperity. A gentle structural high bounds the seaward edge of both basin and asperity, suggesting that they are closely related. The structural high continues to the east and becomes a clear topographic ridge beyond the Kushiro submarine canyon. The seaward slope of the ridge shows seaward-dipping, discontinuous obscure reflections, indicating that the slope is a frontal accretionary prism. The 1952 tsunami source is located in the prism, which is probably uplifting. No indication of large-scale landslide indicates that the extended tsunami source in 1952 is due to tectonic origin.
DE: 3025 Marine seismics (0935, 7294)
DE: 4564 Tsunamis and storm surges
DE: 7221 Paleoseismology (8036)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005